1. Field of the Invention
The present invention is related to a DC/DC boost converter and control method therefor. More particularly, the present invention is applied in a DC/DC boost converter and control method therefor, providing a DC voltage within a specified voltage range to the equipment and thereby avoiding the influence caused by abnormal input DC voltage.
2. Description of the Related Art
The DC voltage source is generally obtained from the AC utility via an AC/DC converter or from a battery bank. The load of DC voltage source may be the motor driver, UPS (Uninterruptible Power Supply) or other electronic related equipment. Most of loads must be operated within a specific voltage range. Otherwise, it may result in abnormal operation of downstream electrical loads even the damage of the loads. A DC voltage supplied by the AC/DC converter may be lower than the specified voltage range due to abnormal ac voltage. Similarly, a DC voltage supplied by the battery bank may be lower than the specified voltage range due to the deep discharge. In order to solve the problem of lower input DC voltage, a DC/DC boost converter is applied to maintain normal operation of loads.
FIG. 1 shows the circuit of a conventional DC/DC boost converter. Referring to FIG. 1, a DC/DC boost converter circuit 1 is connected between a DC voltage source with an input terminal Vin and a voltage output terminal Vout. The DC/DC boost converter includes an inductor 10, a power electronic switch 11, a diode 12 and a capacitor 13. The inductor 10 may be energized when the power electronic switch 11 is turned on. When the power electronic switch 11 is turned off, the stored energy in the inductor 10 will release through the diode 12 into the capacitor 13, then, the capacitor is charged and supplied to the loads. The voltage at output terminal Vout of the DC/DC boost converter circuit 1 is able to supply a voltage higher than that of the input DC voltage at the input terminal Vin by controlling the on/off time of the power electronic switch 11. However, the DC/DC boost converter circuit 1 is operated regardless the input DC voltage is normal or abnormal low voltage caused by the deep discharge of the battery bank or the abnormal ac voltage. Hence, the power loss cannot be avoided regardless the DC voltage source is normal/abnormal in the conventional DC/DC boost converter described above. Generally, the duration of abnormal low voltage in the input DC voltage is only a short interval. However, the conventional DC/DC boost converter circuit 1 is operated regardless the input DC voltage is normal or abnormal. It results in decreasing the power efficiency of the entire equipment. Besides, a larger dimension of a heat dissipation device for the DC/DC boost converter is required to respond to the increase power loss.
The present invention intends to provide a DC/DC boost converter and control method therefore, which actuates when the input DC voltage is lower than the low reference DC voltage and disables when the input DC voltage is higher than the normal voltage, thereby avoid additional power loss in the duration of normal input DC voltage.
The primary objective of this invention is to provide a DC/DC boost converter and control method that the normal input DC voltage can directly pass through a diode to supply a voltage to the output terminal. The DC/DC boost converter provides a step-up DC voltage to the output terminal if the input DC voltage is lower than the specified low reference DC voltage, thereby increasing reliability of supplied voltage for downstream loads. Moreover, the power electronic switch of DC/DC boost converter only actuates when the input DC voltage is lower than the specified low reference DC voltage, and disables when the input DC voltage is high than the normal voltage to minimize power loss, thereby increasing the power efficiency of the entire equipment.
The DC/DC boost converter in accordance with the present invention includes an input terminal and an output terminal. The DC/DC boost converter comprises an inductor, a power electronic switch, a control circuit, a first diode, a second diode and a capacitor. The input terminal, contains a positive node and a negative node, is connected to a DC voltage source such as an AC/DC converter or a battery bank. The output terminal, contains a positive node and a negative node, is connected to loads such as inverters or other DC loads. A serial connection of the inductor and the power electronic switch is connected between two nodes of input terminal. The control circuit is connected to the power electronic switch. The first diode is connected between the connection point of the inductor and the power electronic switch, and the positive node of the output terminals. The capacitor and the second diode are parallel connected between the positive node of the input terminal and the positive node of the output terminal. The power electronic switch is not operated if the input DC voltage is higher than the specified low reference voltage. In this duration, the DC/DC boost converter does not step-up the input DC voltage, the input DC voltage directly passes through the second diode to the output terminals to supply the loads, and thus the voltage of output terminal is approximated as the input DC voltage. The inventive boost converter actuates when the input DC voltage is lower than the specified low reference voltage, and the pulse width modulation control is used to turn on/off the power electronic switch to step-up the DC input voltage to the acceptable voltage of loads in the output terminals. The inductor is energized when the power electronic switch is turned on, and the inductor releases the stored energy when the power electronic switch is turned off. Then the released energy of the inductor passes through the first diode to the capacitor to provide a voltage that supplies a reverse bias to the second diode. Consequently, the output DC voltage is the summation of the input DC voltage and the capacitor voltage. Thus, it accomplishes the step-up function.
The DC/DC boost converter is provided with the function of step-up the input DC voltage and used to increase the operation range of the input DC voltage, thereby avoiding mal-function of electrical equipment due to a lower voltage supplying from the input DC voltage. Moreover, the inventive DC/DC boost converter dose not actuate when the input DC voltage is normal, and it only actuates when the input DC voltage is lower than the specified low reference voltage, It means that the power loss due to the operation of inventive DC/DC boost converter can be avoided if the input DC voltage is in the normal range. Consequently, the power efficiency of the inventive DC/DC boost converter is better than that of the conventional DC/DC boost converter.
Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description and the accompanying drawings.